Staple gun



FIG. 1 is a front, left-side perspective view of a staple gun showing my new design;

FIG. 2 is a left-side elevation view thereof;

FIG. 3 is a right-side elevation view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a front elevation view thereof; and,

FIG. 7 is a rear elevation view thereof. 

The ornamental design for a staple gun, as shown and described. 